Finding the right box
Another major challenge that long COVID-19 researchers face is classification. Many studies are producing data on the syndrome, but if symptoms aren’t collected and classified similarly, trying to compare different studies will be like comparing apples and oranges.
Decisions about how to classify symptoms also affect how patients are grouped together and how the data is analyzed. One big concern: Should patients be grouped by symptom, or should symptoms be grouped by the organs they affect?
It’s a bit of a chicken-and-egg issue, but it gets into the problem of what’s behind long COVID-19 to begin with, said Chow, who began treating Macnofsky after her hospital stay. (The two teamed up to tell Macnofsky’s story in a dual first-person essay published in the scientific journal Open Forum Infectious Diseases.)
“For example, what about fatigue? Do you group everyone with fatigue together? But what if one person’s fatigue is caused by damage to the nervous system, another’s by damage to their heart, and someone else’s by lung damage,” said Chow, who at the start of the pandemic was part of the Centers for Disease Control and Prevention team that went to New York state to confirm COVID-19-associated multisystem inflammatory syndrome in children.
Even in cases where it’s clear the immune system is at fault, fatigue may not have a single cause. Energy-sucking immune activation could explain one person’s fatigue, but post-infection autoimmunity, in which their own tissues are under attack, could be the reason behind another’s, Andrews said.
Trying to find the biological similarities in data taken from these patients would be like trying to compare pages of text written in different languages: more likely to result in gibberish than to identify a helpful pattern.
And sometimes, symptoms may not even be the result of a person’s coronavirus infection. Part of the problem is the often-vague, widely varying collection of symptoms, many of which long COVID-19 shares with other chronic health problems, such as autoimmune diseases or chronic fatigue syndrome. Autoimmune diseases often strike in young adulthood. For some people, SARS-CoV-2 infection and an autoimmune diagnosis are just two pieces of unrelated bad luck.
“In a longitudinal cohort like this, nothing is ever completely clean,” Czartoski said.
Working group members share questions and strategies. Should they classify symptoms by severity score, or follow the CDC’s recommendations to classify symptoms by outcome measures in different areas? Members often draw on their or other members’ expertise in different disciplines, such as adapting questionnaires used by neurologists to assess cognitive difficulties. Czartoski recommended a severity scale long used by HIV researchers to assess how symptoms impact patients’ daily living.
The team also grapples with the challenges of classifying symptoms that may seem focused on a specific organ system, but are actually emblematic of a body-wide problem. Researchers noted that some simplification needs to occur to make it possible to analyze the reams of data that can be collected.
But sometimes it’s unclear what’s causing someone’s symptom — so researchers can’t classify symptoms by underlying cause. What then?
Members also keep an eye on trends in the wider scientific community to see if they can align with areas of growing consensus, the better to compare their results with other studies.
Who’s at risk for symptoms, and how long will they last?
But sorting out the logistical challenges of classification is just the first step. Long COVID-19 researchers want to understand why symptoms develop and who’s at risk. Why do some symptoms affect some patients but not others? Who will have a mild course, and who will suffer greatly? A deeper understanding, they hope, will shed light on why symptoms linger so long for some people, and how to predict how a patient’s experience will unfold.
UW neurologist Dr. Payal Patel is focusing on the cognitive symptoms of PASC.
“I want to know, what is the cause of the symptoms we see in PASC,” said Patel, who studies the continuing effects of infections of the central nervous system, including HIV. “We know PASC affects different organ systems. I’m trying to get a better clinical understanding of how it affects the brain.”
Without this, it’s difficult to give worried patients a clear picture of what they can expect from long COVID. Patel wants to better understand how long such symptoms last, who’s most at risk, and what’s causing them. Is brain fog caused primarily by immune dysfunction? Or could the clotting problems associated with COVID-19 have damaged the cells lining blood vessels in the brain? Patel and a team of scientists have studies underway to answer these questions.
This type of location-specific question can be very difficult to address, Chow noted. It’s relatively easy to take blood samples and look at general patterns of immune cells or antibodies floating through the blood. But what about problems that are occurring at a hard-to-reach spot, like tiny blood vessels in the brain or lungs?
Some working group members focus their research questions on specific areas of the body. With Patel, Andrews is trying to understand who’s most at risk for cognitive and physical impairments after COVID. Some patients’ fatigue is related to muscle wasting, known medically as sarcopenia, and Andrews wants to know what’s behind that and who’s at risk.
Role of the immune system in long COVID-19
Since it became understood that an overactive immune response (known as a “cytokine storm”) lurks behind some of COVID-19’s most dire complications, scientists have begun digging deeper into how the immune system responds to SARS-CoV-2. Macnofsky herself participated in a Benaroya Research Institute study looking at the immune response to the novel coronavirus.
Bender Ignacio's working group is drawing on the Hutch’s longstanding expertise in immunology and infectious diseases and looking to the immune system for answers.
“We’re studying what natural infection looks like over time,” said Fred Hutch immunologist Dr. Maria Lemos, who studies immune responses in mucosal tissue like vaginal and nasal surfaces, where we first encounter many viruses. “People could have cold symptoms for nine days, then four moths later they’re diagnosed with a lung condition or a heart condition.”
To understand why, she and others on McElrath’s team are mapping the immune response to SARS-CoV-2 infection as it unfolds over months. With collaborators at Emory University in Atlanta, they’re charting the rise and fall of antibodies against the virus and how different immune-cell populations grow, shrink and morph over time.
By describing how these responses differ between people who did and did not develop long COVID-19, the researchers hope to identify key biomarkers, like specific inflammatory proteins, that help predict which patients will have persistent problems. Such biological predictors could help doctors intervene early, either to help connect patients with the right services to help them deal with symptoms, or (once scientists crack this problem) stave it off entirely.
McElrath’s team, with collaborators at Emory University and the Seattle-based Allen Institute for Immunology, has revealed some tantalizing immunological patterns, Lemos said, which the group posted on the preprint server biorxiv.org. The immune trajectory in many long-haulers looks startlingly unlike that seen in people who recover quickly and permanently.
“The alarm system of the immune system doesn’t get turned on as quickly in these people — but surprisingly it seems to remain on for way longer,” Lemos said. They’re currently putting together a paper for peer review at a scientific journal.
On top of this project, Moodie is working with investigators the Allen Institute to identify immunological signatures, including cellular features like proteins and gene expression, that distinguish long COVID-19 from acute COVID-19. Some patients — including Macnofsky — report improvement of symptoms after vaccination for COVID-19, and Moodie and her collaborators want to understand how vaccination may help their bodies resolve their chronic, damaging immune responses.
(Whether prior COVID-19 vaccination helps protect against developing long COVID-19 is still being explored. A recent study in The Lancet suggests that vaccinated people are less likely to have long-lasting symptoms after SARS-CoV-2 infection.)